1. Technical Field
This invention relates generally to electronic devices having antennas for transmission of communication signals, and more specifically to an electronic device having dual antennas, wherein the dual antennas are autodiplexing in that they direct power to a lesser loaded of the antennas.
2. Background Art
Two-way communication devices, such as mobile telephones, two-way radios, and personal digital assistants, each use antennas to transmit and receive radio-frequency communication signals. These antennas communicate with wide area network towers, local area network base stations, and even other devices directly, to transmit and receive data. The antennas allow the device to be truly wireless, in that all communication may occur through the air.
While once large, retractable devices, the antennas found on most common communication devices are quite small today. The antennas generally come in one of two forms: stub and internal. With a stub antenna, a small protrusion emanates from the electronic device. With the internal antenna, the antenna itself is completely embedded within the device, thereby creating a sleeker, stylish look.
One problem experienced by both stub and internal antennas is that of loading. Using a mobile telephone as an example, when a person places a call, they generally hold the phone close to their ear with a hand. As today's mobile telephones are becoming quite small, sometimes the hand effectively envelops the device. Consequently, the antenna within the device must transmit power either through or around the hand to communicate with a tower, base station, or other device. The hand being placed next to the antenna “loads” the antenna, thereby making it more difficult for the antenna to “talk” to other devices.
There are two prior art solutions to the loading problem. The first solution is to simply make the antenna bigger. For example, in prior art two-way radios, the antenna was a long, extendable metal device. Where the antenna extends beyond whatever is loading it, the loading effect is reduced. This solution is not feasible in today's modern electronic devices, however, as a two-foot antenna is not practical on a three-inch mobile telephone. Further, high operating frequencies may not be suitable for an antenna that is very long compared with its operating wavelength.
The second prior art solution is to increase the transmission power whenever the antenna is loaded. The problem with this solution is that rechargeable batteries generally power these mobile devices. As such, an increase in transmission power means an increased load on the battery. This increased load means less “talk-time” between recharging, which can be frustrating to users of these devices.
There is thus a need for an improved antenna for electronic communication devices capable of operation under loaded conditions.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.